Process for producing a formed lightweight metal component

ABSTRACT

The disclosure relates to a process for producing a formed lightweight metal component from a 6000 series or 7000 series aluminum alloy, having the process steps of heating a sheet metal blank, then homogenizing a solution annealing temperature, quenching the heated blank, and forming the heated blank into a component.

RELATED APPLICATIONS

The present application claims priority of German Application Number 102018104326.0 filed Feb. 26, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD

The disclosure relates to a process for producing a formed lightweight metal component from a 6000 series or 7000 series aluminum alloy.

BACKGROUND

The prior art discloses producing formed components, like motor vehicle components, from lightweight metal.

For this purpose, there are firstly aluminum alloys that are solidified at low temperature. In automobile construction, these are generally 5000 series aluminum alloys, which are referred to as materials of natural hardness or rolling hardness.

Also known, however, is the working of aluminum alloys that can be hardened by thermal treatment processes. In automobile construction, these are generally 6000 series or 7000 series aluminum alloys. These are called heat-treatable aluminum alloys.”

In the case of aluminum alloys that are heat-treatable, the solidification mechanisms are solid solution hardening and precipitation hardening. Solid solution solidification is brought about by the incorporation of interstitial lattice atoms in the aluminum lattice. For this purpose, an aluminum alloy is brought to solution annealing temperature and then quenched. In this case, the state of the solid solutions is frozen at first. The material also has good formability in this state. The oversaturated solid solutions precipitate a second phase of the alloy elements with time, which increases the hardness and strength of the material. At the same time, however, there is a decrease in unformability.

Solution annealing temperatures in the case of 7000 series aluminum alloys are about 480° C., and in the case of 6000 series aluminum alloys about 540° C.

It is now necessary, for production of motor vehicle components, to provide high throughput rates in a production plant.

Nowadays, for this purpose, semifinished products in a composite or with prior individualization are typically cold-formed in a forming mold. Hardening is then generally effected in a later heat treatment operation, for example during the later supply of heat in the application and hardening of the paint system. Also additionally known is heating of the semifinished products and/or forming molds. The heating techniques used for this purpose, typically continuous furnaces, generally limit the manufacturing rate since, for process- and plant-related reasons, a higher throughput has to be achieved via an extension of the furnace length, which leads to technical (e.g. flexibility, susceptibility to faults) and economic (e.g. level of investment, operating costs) trade-offs. The effect of this is that the throughput rate is much lower at 2-10 times lower than in the case of cold forming.

WO 2010/032 002 A1 discloses a process for forming sheets from aluminum alloys. In this process, an aluminum blank is heated to solution annealing temperature in a heating station and then placed into a cold forming mold within 10 seconds.

DE 10 2012 221 602 A1 and DE 2016 208 014 A1 also disclose production processes for components from aluminum alloys.

Further processing methods for sheet metal components are known from DE 10 2014 215 365 A1, US 2017/0 081 748 A1, EP 2 977 472 A1 and DE 10 2017 109 613 A1.

SUMMARY

It is an object of at least one embodiment of the disclosure, proceeding from the prior art, to provide a process by which it is possible to bring heat-treatable aluminum alloys to solution annealing temperature at high throughput rates quickly, by a reliable process and efficiently, and the process is also to be retrofittable in already existing plants.

The aforementioned object is achieved in accordance with the at least one embodiment.

The process for producing a formed lightweight metal component, like a motor vehicle component, from a precipitation-hardenable lightweight metal alloy, from a 6000 series or 7000 series aluminum alloy, comprises the following process steps:

-   -   providing a blank, the blank being a sheet metal strip, a sheet         metal blank, an extruded profile or a preformed component,     -   at least partly preheating the blank by contact heating to a         temperature not more than the solution annealing temperature in         a first heating station,     -   subsequently homogenizing to solution annealing temperature in a         second heating station, like a furnace,     -   quenching the heated blank within less than 30 s downstream of         the second heating station,     -   forming the heated blank to the formed component during or after         the quenching.

First of all, a blank is thus provided. In at least one embodiment, this may be an extruded profile, for example a profile that has single or multiple chambers in cross section. However, the blank may also be a sheet metal blank. The blank may also be a preformed component, i.e. a preform that has been preformed from a sheet metal blank, for example. The blank may also be a sheet metal strip.

According to at least one embodiment, at least partial preheating of the blank by contact heating is now conducted. This is accomplished in a first heating station that takes the form of a contact heating station. It is also possible to conduct complete solution annealing. The preheating is conducted at least partially to completely, to a temperature not more than the solution annealing temperature of the aluminum material used.

The contact heating station makes it possible to implement a kind of “boost” effect. The contact heating can introduce a large amount of heat into the blank within a short time. As a result, a subsequent second heating operation to a temperature equal to or higher than the solution annealing temperature can be conducted more quickly, more efficiently and in a more controlled manner.

As a result of the at least partial preheating in the first heating station, the blank is already at least partially at a temperature greater than 200° C., or at a temperature between 300° C. and 500° C., or at about at least 300° C., or between 300° C. and 450° C. “The at least partial” means that the contact sites on the blank that abut contact plates or tool surfaces of the contact heating station are brought to this temperature. The solution annealing temperature in the blank is already at least partially attained in the first heating station. For 7000 series aluminum alloys, this is between 400° C. to 500° C. For 6000 series aluminum alloys, this is 500° C. to 600° C. The subsequent input of heat in the second heating station may thus be over a shorter period of time.

Any excess temperature in the second heating station can likewise be lowered, which also reduces the energy costs. As a result, however, the blanks on conclusion of the second heating station are reliably at least the solution annealing temperature. Thus, it is also possible to shorten the cycle times and hence the length in the case of a furnace, or continuous furnace, in the second heating station.

In at least one embodiment of the disclosure, already existing plants can be retrofitted in a simple manner by connecting a corresponding first heating station in the form of a contact heating station upstream in an existing heating station, for example in an existing continuous furnace. This can be retrofitted onto already existing plants. The throughput rate of the plants can thus be increased. It is thus also possible to further develop plants that have to date been designed solely for the processing of 7000 series aluminum alloys, for example, for the processing of 6000 series aluminum alloys having a higher solution annealing temperature as well, without losses in the throughput rate.

The second heating station, i.e. on attainment of at least the solution annealing temperature, is followed downstream by a forming operation to produce the formed component. This forming operation can be conducted immediately after the second heating operation. The formed lightweight metal component produced by the process of at least one embodiment can also be called component or formed component.

The forming is conducted as a cold forming operation. For this purpose, the blank heated to solution annealing temperature is quenched immediately downstream of the second heating station. This quenching is effected within a period of less than 20 seconds, or less than 10 seconds, but at least one second after the second heating operation. It is possible here, for example, for a quenching unit to be connected downstream of the second heating station. The quenching can be effected, for example, by means of a medium, for example air and/or water. This can be accomplished by jetting and/or spraying and/or dipping. Contact cooling can also be conducted. This is an option in the case of sheet metal blanks. Quenching may be conducted by dipping into a cooling medium.

The quenching can also be conducted in the forming mold. For this purpose, the blank that has been heated downstream of the second heating station will be inserted into a cold forming mold. “Cold” means to room temperature, but at least such that the forming mold has a temperature below 100° C., below 80° C., below 50° C. and below 30° C. However, the forming mold at least be at 100° C. For this purpose, the forming mold may also be actively cooled, such that final quenching of the formed component is accomplished in the forming mold. The component produced is thus removed from the forming mold at a temperature below 100° C., below 80° C. and below 50° C.

If the quenching has been conducted separately, the quenching operation is then immediately followed by a forming operation. The quenching is likewise effected within a cycle time. The first heating station, the quenching unit and the forming unit all work at the same cycle rate. This cycle rate is less than 10 seconds, less than 8 seconds, or between 5 and 7 seconds, the cycle time may also be 6 seconds.

It has been found for the first heating station itself to be in multistage form, in such a way that in a first stage a first heating operation takes place within the cycle time mentioned, while a further heating operation is conducted in the next cycle in an immediately subsequent second stage of the heating station. Further stages may optionally follow, according to cycle time requirements, before the blank is homogenized at the solution annealing temperature in the second heating station.

The component is thus also inserted into the forming mold from the quenching unit within less than 20 seconds, or less than 10 seconds, but at least within a second, and formed here within the appropriate cycle time. The forming operation is then followed by an age hardening process. This is conducted as a cold age hardening process and lasts for several days.

The first heating station is operated with contact plates. In that case, these contact plates are placed onto a blank from above and below and transmit their temperature to the sheet metal blank/to the blank to be heated by means of conduction of heat. For this purpose, the contact plates are at an excess temperature. For this purpose, the contact plates are at a temperature greater than 300° C., greater than 450° C. However, the contact plates have a temperature less than 650° C. The contact plates themselves are heated, for example by resistive heating. Therefore, the contact plates themselves take the form of resistance heating. The contact plates themselves may also in turn be heated by an inductor. It is likewise possible, for example, to introduce heating cartridges or the like into the contact plates in order to heat the contact plates.

In the partial preheating operation, it is thus possible to introduce at least a local temperature in the blank of 200° C. to 500° C., or 300° C. to 450° C. When the blank is an extruded profile, the abutting surfaces of the blank are brought to this temperature with the contact plates. In a subsequent heating operation in a second heating station, however, conduction of heat occurs within the blank itself, and hence better and quicker homogenization and heating to solution annealing temperature.

However, the blank is at least heated at its contact surfaces to at least 200° C., to more than 300° C.

This is then followed by transfer into the second heating station, which may take the form of a furnace or a continuous furnace. There may be a linear drive or a linear transfer system here, such that the first heating station is connected immediately upstream of the second heating station. Thus, easy refitting or retrofitting of a heat treatment line can be undertaken for production of a formed lightweight metal component. It is also possible to provide a transfer system between the first and second heating stations, or a step-lift drive.

In at least one embodiment, in the heating of sheet metal blanks, at least two sheet metal blanks are stacked directly one on top of another and are introduced into the first heating station. The at least two superposed sheet metal blanks are thus heated simultaneously.

In this way too, the production rate can be increased again.

Before insertion into a forming mold, a lubricant can be applied to the heated blank. In a separate quenching station, the lubricant is applied after the quenching and prior to the forming.

In addition, the contact plates in the first heating station itself are in turn spring-mounted. This achieves better abutment contact to the blank to be heated, which in turn improves the heat transfer. The contact plates themselves are in two-dimensional form. This serves to heat blanks in the form of sheet metal blanks or else of blanks as extruded profiles, where the extruded profiles have two-dimensional outsides or contact surfaces to the contact plates. It is also possible to choose contact plates adapted to the shape. This embodiment is possible in the case of preformed components or else profiles that do not have a straight outline. For this purpose, the contact plates on the first heating station are exchangeable, via a quick-change system. For example, the contact plates are arranged on a plate, by mechanical coupling in the form of screws. The contact plates of the heating station may also be slotted or segmented, such that different thermal expansions are compensated for.

The contact plates may then, if required, be changed in a simple manner in order to adapt the forming line to a different blank and/or a different outline of a blank or a different size of a blank.

It is thus possible to reach the solution annealing temperature homogeneously in the blank. At the same time, however, the energy input and the length of a continuous furnace can be reduced, with an identical or improved outcome in the attainment of a homogeneous solution annealing temperature at the end of the thermal treatment.

This also reduces shutdown times or reworking times in a hot forming line.

In at least one embodiment, a further heating station may be inserted between the first heating station and the second heating station. This further heating station takes the form of a contact heating station. A two-stage preheating operation may thus take place. This would be described further up as a multistage preheating operation.

Other features and properties of the present disclosure are the subject of the description which follows. Configuration embodiments are illustrated in the schematic figures.

BRIEF DESCRIPTION OF THE DRAWINGS

For an understanding of embodiments of the disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 a forming line according to prior art,

FIG. 2 a schematic diagram of a process sequence, and

FIG. 3 a forming line in accordance with at least one embodiment of the disclosure.

In the figures, the same reference numerals are used for identical or similar components, even though a repeated description is omitted for reasons of simplification.

DETAILED DESCRIPTION

FIG. 1 shows a known forming line 1 for production of a formed component 2 produced from lightweight metal. For this purpose, a continuous furnace 3 is connected upstream of a forming station 4. The forming station 4 takes the form of a thermoforming apparatus or forming press. The continuous furnace 3 then has a length 5 into which inserted blanks 6, in the form of profiles here, are inserted and then pass through the continuous furnace 3. At the end of the continuous furnace 3 is provided a transfer system 7, for example a linear conveyor, in order to transfer the blanks 6 that have been heated to a temperature in the continuous furnace 3 into or through a quenching unit and further into the forming mold. These are formed here and then removed from the forming mold.

FIG. 2 then shows a process sequence of at least one embodiment. First of all, a blank 6 is provided. In this example, a hollow profile has likewise been used. This profile may be produced, for example, by extrusion and cutting-to-length to give individual profile pieces. The profile is then inserted into a first heating station 8 in the form of a contact heating station. The heating station 8 itself has contact plates, here in the form of an upper contact plate 9 and a lower contact plate 10. A heat source 16 may be provided in the contact plates. The contact plates are then closed in a direction 11, such that the contact surfaces 12 of the contact plates come to rest on contact surfaces 13 of the blank 6. There is partial introduction of heat here by conduction of heat. Therefore, the heat of the contact plates 9, 10 is released to the blank 6 by means of conduction of heat. Thereafter, the blank 6 thus preheated is passed onward into a second heating station 14, or a continuous furnace. This second heating station 14 has a distinctly shorter length 15 compared to the continuous furnace 3 according to FIG. 1. The blank 6 thus heated is then transferred through or into a quenching unit 17 and cooled, for example, to less than 250° C. From the quenching unit 17, the blank 6 is then transferred into a forming tool 4 and formed therein.

Rather than the quenching apparatus between the second heating station 14 and the forming mold 4, it is also possible to provide for a quenching operation to take place at an earlier stage in the forming mold 4.

The forming line 1 of at least one embodiment is shown once again in FIG. 3. First of all, the blanks 6 are inserted into the first heating station 8 and heated therein by means of contact heating within a very short time. At the same time, it is also possible to heat two or more blanks 6 in the first heating station 8. The blanks 6 that have thus been preheated are then transferred directly to the second heating station 14 and brought, in a homogeneous manner to solution annealing temperature therein. This may be followed by a quenching operation, which is not shown in detail. This in turn is then followed directly by a forming operation in the forming mold 4. Alternatively, the blank 6 may also be transferred from the second heating station 14 directly in the warm state into the forming mold 4. In this case, the forming mold 4 would in turn be followed by a quenching operation which is not shown in detail. It is likewise not shown that a further heating station may be connected intermediately between the first heating station 8 and second heating station 14, such that the preheating is conducted in multiple stages.

The foregoing description of some embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings. The specifically described embodiments explain the principles and practical applications to enable one ordinarily skilled in the art to utilize various embodiments and with various modifications as are suited to the particular use contemplated. It should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the disclosure. 

1-9. (canceled)
 10. A process of producing a formed lightweight metal component from a precipitation-hardenable aluminum alloy, the process comprising: providing a blank of the aluminum alloy, the blank being a sheet metal strip, a sheet metal blank, an extruded profile or a preformed component, at least partly preheating the blank by contact heating to a temperature not more than a solution annealing temperature of the aluminum alloy in a first heating station, subsequently homogenizing the at least partly preheated blank to the solution annealing temperature by heating the at least partly preheated blank in a second heating station, quenching the heated blank within less than 30 seconds downstream of the second heating station, and forming the heated blank to a formed component during or after the quenching.
 11. The process as claimed in claim 10, wherein the heated blank is quenched in said quenching within a period of less than 20 seconds after the second heating station and is immediately cold-formed in said forming.
 12. The process as claimed in claim 10, wherein the first heating station has contact plates, where the contact plates have a temperature greater than 450° C. in said contact heating.
 13. The process as claimed in claim 10, wherein, in the preheating, the aluminum alloy is preheated to a temperature of 200 to 560° C.
 14. The process as claimed in claim 10, wherein the blank downstream of the second heating station is maintained at a temperature not less than the solution annealing temperature.
 15. The process as claimed in claim 10, wherein the second heating station is a continuous furnace.
 16. The process as claimed in claim 10, wherein the cycle time for each of the forming and preheating is less than 30 seconds.
 17. The process as claimed in claim 12, wherein the contact plates of the first heating station are spring-mounted and/or the contact plates are two-dimensional or fitted to a shape of the blank to be preheated.
 18. The process as claimed in claim 10, wherein the heating in the second heating station maintains the solution annealing temperature for a duration of 5 seconds to 5 minutes.
 19. The process as claimed in claim 10, wherein the heated blank is quenched in said quenching within a period of less than 10 seconds after the second heating station and is immediately cold-formed in said forming.
 20. The process as claimed in claim 10, wherein the cycle time for each of the forming and preheating is less than 20 seconds.
 21. The process as claimed in claim 10, wherein the cycle time for each of the forming and preheating is between 5 and 15 seconds.
 22. The process as claimed in claim 10, wherein the heating in the second heating station maintains the solution annealing temperature for a duration of 10 seconds to 3 minutes.
 23. The process as claimed in claim 10, wherein the heating in the second heating station maintains the solution annealing temperature for a duration of 20 seconds to 2 minutes.
 24. The process as claimed in claim 10, wherein, in the preheating, the aluminum alloy, which is a 7000 series aluminum alloy, is preheated to not more than 480° C.
 25. The process as claimed in claim 10, wherein, in the preheating, the aluminum alloy, which is a 6000 series aluminum alloy, is preheated to not more than 540° C.
 26. The process as claimed in claim 10, wherein the aluminum alloy is a 7000 series aluminum alloy, and the blank downstream of the second heating station is maintained at 460 to 480° C.
 27. The process as claimed in claim 10, wherein the aluminum alloy is a 6000 series aluminum alloy, and the blank downstream of the second heating station is maintained at 520 to 540° C. 